Fix 500 error for old (somewhat) MRs

1 files changed, 5 insertions, 3 deletions

diff --git a/lib/gitlab/diff/position.rb b/lib/gitlab/diff/position.rb
index bd0a9502a5e..ccfb908bcca 100644
--- a/lib/gitlab/diff/position.rb
+++ b/lib/gitlab/diff/position.rb
@@ -94,7 +94,9 @@ module Gitlab
       end
 
       def diff_file(repository)
-        @diff_file ||= begin
+        return @diff_file if defined?(@diff_file)
+
+        @diff_file = begin
           if RequestStore.active?
             key = {
               project_id: repository.project.id,
@@ -122,8 +124,8 @@ module Gitlab
 
       def find_diff_file(repository)
         return unless diff_refs.complete?
-
-        diff_refs.compare_in(repository.project).diffs(paths: paths, expanded: true).diff_files.first
+        return unless comparison = diff_refs.compare_in(repository.project)
+        comparison.diffs(paths: paths, expanded: true).diff_files.first
       end
 
       def get_formatter_class(type)